As a method for purifying fermentation alcohol liquid discharged from a fermenter, a conventional method is separating and concentrating an alcohol-water mixture from the fermentation alcohol liquid (mash) by a mash column; further concentrating the alcohol-water mixture substantially to an azeotropic composition by a concentrating column; and then treating it by an azeotropic distillation column to give high-purity anhydrous alcohol.
Patent Reference No. 1 has disclosed a method using a membrane separator in place of an azeotropic distillation column, wherein an alcohol-water mixture concentrated substantially to an azeotropic composition by a distillation column is evaporated in an evaporator and introduced to the membrane separator to be purified.
Patent Reference No. 2 has also disclosed the identical system to that in Patent Reference No. 1. On the system disclosed in the reference, when a distillate from a distillation column is heated by introducing into an evaporator, an alcohol/water mixed vapor with a higher pressure than an operating pressure of the distillation column is generated, and the high-pressure vapor is introduced to a membrane separator, so that the membrane separator can be very efficiently operated. The reference has described that the distillation column is operated such a manner that 10 to 90% of a condensate obtained by condensing the distillate discharged from the top of the distillation column is refluxed to the distillation column, but has not described preferable operating conditions in view of an energy efficiency. In Examples therein, 10% by weight of an ethanol aqueous solution is concentrated to 80% by weight by feeding to a distillation column, and the condensate is evaporated in an evaporator and fed to a membrane separator.
Citation List
Patent Literature
Patent Reference No. 1: Japanese Laid open publication No. S63-258602.
Patent Reference No. 2: WO 2004/073841.